Filters that have multiple coupled resonators are well suited for use in communication systems. While the filters have low insertion loss, high stop-band isolation and other desirable performance characteristics, the filters are extremely sensitive to mis-tuning of the coupled resonators. Typically, the resonators within the filter require adjustment to achieve a specified filter response. Mechanically tuned waveguide filters, for example, include adjustment screws for tuning multiple resonant cavities within the filter.
Known filter tuning methods involve adjusting or tuning the resonant frequency of each resonator until the specified filter response is achieved. The adjustments are made as the overall filter response is observed on a display. However, due to coupling between resonators, the effect of tuning one resonator on the overall filter response is not isolated from the effect of tuning other resonators within the filter. This causes interactions between the resonators that influence the overall filter response in an unpredictable fashion, making it difficult to tune the filters to achieve the specified filter response.
According to the preferred embodiment of the present invention a tuning method isolates the characteristics of each coupled resonator of a filter, enabling a specified filter response to be easily achieved by adjusting the coupled resonators according to response criteria. A target frequency response is defined for a filter having multiple coupled resonators. A time domain response is derived from the target frequency response. From the time domain response, a gating function is generated for each of the resonators. A stimulus signal is provided to the filter and the response to the stimulus signal is measured. The gating functions are then applied to isolate the response characteristics of each of the coupled resonators enabling each resonator to be adjusted according to response criteria chosen to achieve a specified filter response when the response criteria are satisfied.